The present invention relates to a cutoff valve for pistons of hydraulic self-adjusting devices, in particular for use in hydraulic-self-adjusting devices designed for the permanent, automatic adjustment of the length of control cables.
Hydraulic self-adjusting devices for the permanent, automatic adjustment of the length of control cables are widely known and generally consist of steel cables provided with a protective sheath and attached to an actuating mechanism, such as a pedal for example, with an associated mechanism, such as the clutch of a car for example. These self-adjusting devices carry out adjustment independently of the initial adjustment of the length of the control cable, which is normally carried out when the cable is fitted by means of devices designed for the purpose that operate only during said initial adjustment process.
The Spanish patent P 9002014 describes a hydraulic self-adjusting device which consists basically of a cylindrical main body, joined to the mechanism to be actuated, and an adjustment rod, one of the ends of which, the external end, is attached the control cable, whilst the other end, the internal end, has a piston provided with a cutoff valve, said piston defining two semi-chambers inside the main body between which the hydraulic fluid can flow. Furthermore, said device comprises an adjustment spring and volumetric compensation means. This devices operates in such a way that the required increase in length of the control cable as a result of the mechanical demands placed on the mechanism it actuates (for example the progressive wear of the facing on the clutch plate of a car) is provided by the increase in length of the portion of the adjustment rod which protrudes from the main body of the self-adjusting device.
One of the cutoff valves for such hydraulic self-adjusting devices which is described by said patent P 9002014 comprises a through element, a cutoff element and an opening spring which works in compression, these elements being arranged coaxially with the adjustment rod. The purpose of the opening spring is to maintain the cutoff valve open so that the liquid fluid can flow between the two semi-chambers of the main body when the adjustment rod is not being pulled by the control cable. The cutoff valve establishes the hydraulic communication between the two semi-chambers by means of the close fit between the cutoff element of the valve and the inner wall of the main body.
This cutoff valve described by the Spanish patent P 9002014 suffers from the drawback that it consists of a large number of components, which increases the cost of production of the valve as well as its assembly.